1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a liquid crystal display (LCD) and a method of driving the same, and more particularly, to an LCD with an improved frame rate and brightness and a method of driving the same.
2. Description of the Related Art
LCDs display images by applying a voltage to each pixel on a liquid crystal panel according to an input image signal and adjusting transmittance of light for each pixel and are used in notebooks, desktop computers, LCD-TVs, and mobile communication terminals. An LCD is a non-emissive flat panel display that needs external light to produce images since it does not emit light. Thus, an LCD requires a backlight unit that is located behind a liquid crystal panel and a driver unit for driving the liquid crystal panel.
FIG. 1 is a schematic diagram of a related LCD. Referring to FIG. 1, the related LCD includes a liquid crystal panel 10, a backlight unit 35 supplying light to the liquid crystal panel 10, and a driver unit driving the liquid crystal panel 10. The liquid crystal panel 10 includes m×n liquid crystal pixels arranged in a matrix form, m data lines D1 through Dm and n gate lines G1 through Gn arranged to intersect each other, and thin film transistors (TFTs) disposed at positions where the data lines D1 through Dm and the gate lines G1 through Gn intersect. The driver unit includes a data driver 15 supplying data signals to the data lines D1 through Dm, a gate driver 20 supplying scan signals to the gate lines G1 through Gn, a timing controller 25 controlling the data driver 15 and the gate driver 20 using a synchronization signal, and an inverter 30 driving the backlight unit 35.
The TFT formed in each liquid crystal pixel performs a switching operation according to a data signal supplied from a corresponding one of the data lines D1 through Dm in response to a scan signal supplied from a corresponding one of the gate lines G1 through Gn.
The timing controller 25 uses a vertical/horizontal synchronization signal to generate control signals for the gate driver 20 and the data driver 15. The data driver 15 converts digital image signals into analog data signals in response to the control signal received from the timing controller 25 and supplies the analog data signals to the data lines D1 through Dm. The gate driver 20 sequentially supplies scan pulses to the gate lines G1 through Gn in response to the control signal received from the timing controller 25 and selects horizontal lines of the liquid crystal panel to which data signals are supplied. The inverter 30 supplies a driving voltage to the backlight unit 35. The backlight unit 35 generates a beam corresponding to the driving voltage and supplies the beam to the liquid crystal panel 10.
TFTs are the most common type of switching devices used in LCDs, and LCDs using TFTs as switching devices are referred to as TFT-LCDs. Producing a color image in a LCD is accomplished by spatial division in which each pixel represents one of red (R), green (G), and blue (B) or time division in which every pixel sequentially represents R, G, and B colors. When the time division method is used, the LCD includes R, G, and B light sources that are sequentially turned on. More specifically, after all pixels are scanned according to the operation of a gate driver and a data driver, a red light source is turned on and then off. All pixels are scanned again and then a green light source is turned on. The green light source is turned off and all pixels are scanned again before a blue light source is turned on. On the other hand, according to the spatial division method, R, G, and B color filters are disposed in respective regions corresponding to pixel electrodes to realize respective colors. Thus, when an LCD operates at the same frame frequency, the time division method requires a shorter time during which each color light source is turned on than taken using the spatial division method.
Meanwhile, to display a moving image, the response rate and operating speed of liquid crystals must be equal to or greater than the number of frames in the moving images. Further, LCD frame frequency must be increased to realize a high-resolution precise moving image. When the response rate and operating speed of liquid crystals are low, the screen may appear crumpled or scattered because there is insufficient time to arrange the liquid crystals in a liquid crystal panel. Moreover, because the response rate and operating speed of liquid crystals can be increased only by limited degree, it is also difficult to increase frame frequency.
FIG. 2 illustrates arranging lines of a liquid crystal panel with respect to time showing a process of aligning liquid crystals according to data supplied from a data driver and corresponding color light being supplied with respect to time.
The time during which liquid crystals are switched from an “off” state to an “on” state according to a data signal is called rising time (τ) and the time during which all liquid crystals are switched from an “on” state to an “off” state is called falling time. The designations S, U, and T denote a rising interval, an interval during which the liquid crystals remain in the on state, and a falling interval, respectively. A backlight unit supplies light during interval U. This process is repeated sequentially for R, G, and B colors. For example, when the total time taken for the liquid crystal panel to display an image frame is 16 msec, data is supplied for less than 2 msec, and all TFTs are turned on for less than 8 msec to align liquid crystals, light must be supplied for less than 6 msec. Thus, as frame frequency decreases, the time during which light is supplied becomes shorter, thus resulting in significant degradation of brightness. Further, as LCD screen size increases, brightness degradation becomes more severe because the time taken for the liquid crystal panel to turn on increases.